In the nitride semiconductor laser, crystal defect or dislocation of a waveguide causes electron-hole pairs to make non-radiative recombination therein. Ideally, considering the laser function, the dislocation density in the waveguide may be 106/cm2 or less, preferably 104/cm2 or less. However, in the present situation, the dislocation density can not be reduced to less than 106/cm2 by using a vapor phase epitaxial growth (MOCVD and HVPE) or by using a repeated ELOG (Epitaxial lateral overgrowth), because the waveguide is grown on a heterogeneous substrate, such as sapphire substrate or SiC substrate.
To form a light emitting device comprising nitride semiconductor on a sapphire substrate or a SiC substrate without crack, the nitride semiconductor having the reduced dislocation density is required to be grown in the form of a thin layer on a sapphire substrate or a SiC substrate. If the nitride semiconductor is grown in the form of a thick layer on the substrate such as sapphire substrate etc, the curving of the substrate will be bigger, which leads to higher probability of crack occurrence. However, the nitride semiconductor in the form of a thin layer, in which the dislocation density is reduced, has not been realized by the vapor phase epitaxial growth.
To summarize the above, there has been a limitation to form a nitride semiconductor light emitting device (especially a laser device) by the vapor phase growth. Moreover, regarding the light emitting diode, in case that the higher luminance and higher output are required, the crystal dislocation of the substrate and of the intermediate layer will be a serious problem.